After going all-in with the "bow in the vague direction of France" portion of vermouth, I actually believe a good balance of gin and vermouth creates the perfect martini.

3 parts gin (see below)
1 part dry vermouth (Dolin, or sub in Lillet Blanc)
1 dash olive brine

Shake with cracked ice, strain and pour into a cocktail glass.

Garnish with an olive or two on a skewer, or cocktail onions for a gibson. The Columbia Room serves their signature martini with a twist and a dash of orange bitters.

On gin - I often mix my gins in a martini, have 2 parts of a dry gin (CapRock Organic Dry (Colorado, http://www.peakspirits.com/index.php), Green Hat (DC, http://greenhatgin.com/) or Botanist or Damrak) and 1 part wetter gin, I use Catoctin Creek (Virginia, http://catoctincreekdistilling.com/).

Some of my favorite modifications from this are among the following (mix and match!):

• Sub in Lillet Blanc for the vermouth, for a less vermouthy taste
• A dash of rosemary simple syrup
• A dash of Clear Creek Douglas Fir Eau-de-vie for a sprucy spring
• The classic (and arguably original) swapping out the olive and brine for a lemon peel twist (make sure to twist over the glass to extract the oils, or add a dash of lemon bitters

Some variants on the martini by famous folk: http://www.mentalfloss.com/blogs/archives/20029

http://en.wikipedia.org/wiki/Martini_(cocktail)

Tom Lehrer closes out his "Bright College Days" song with a memorable chant -- "Hearts full of youth! Hearts full of truth! Six parts gin to one part vermouth!"